1. Field of the Invention
The present invention relates to a process for preparing lankacidin carbamate derivatives having antimicrobial activities.
2. Prior Art
Lankacidines are antibiotics which are produced and accumulated by cultivating a Streptomyces strain and have the structure represented by the formula: ##STR2##
In the above formula, where Ra is COCH.sub.3, the compound is lankacidin A, and where Ra is H, it is lankacidin C. Known derivatives of the lankacidins are, for example, those having an ester group at the 8 and/or 14 positions of lankacidin C [see Kagaku & Seibutsu (Chemistry and Organism, Vol. 15, pp. 337-342 (1977)): Journal of the Takeda Research Laboratories, Vol. 41, pp. 81-113 (1982)], those having an acyloxy group or the like at 8 and/or 14 positions thereof [see The Journal of Antibiotics, Vol. 26, pp 647 (1973)], and those having 8-substituted alkyl ester, 8-carbonate ester and 8-substituted carbamate (Japanese Published Unexamined Patent Application No. 240687/1987). Japanese Published Unexamined Patent Application No. 240687/1987 also discloses processes for preparing lankacidin A carbamate in which lankacidin A is reacted with isocyanates, and pentachlorophenoxy- or 2,4,5-trichlorophenoxycarbonate of lankacidin A is reacted with amines. These known processes are, however, required to use highly toxic isocyanates or expensive polyhalogenophenoxycarbonylchloride, while their yields are not satisfactory.